Method and apparatus for in situ inspection of reformer tubes

ABSTRACT

A method and apparatus for accurately determining the interior profile of cylindrical objects such as reformer catalyst tubes is described. The radius of the tube is measured from the axis of the tube for each point of the interior surface by calculating the angle of a reflected light beam and the deviation thereof. A first embodiment reflects an light beam off of the interior surface of the cylinder and measures the angle of the light reflected from the interior of the cylinder. A second embodiment removes rotating parts by using a cone mirror to reflect a ring of light onto the interior of the cylinder. Signal processing means are provided to reduce surplus signals allowing transmission of only useful information.

CLAIM FOR PRIORITY

This application claims priority under 35 § U.S.C. § 120 to applicationSer. No. 09/713,415, filed Nov. 11, 2000, entitled “Method And ApparatusFor In Situ Inspection of Reformer Tubes,” which is hereby fullyincorporated by reference.

CROSS REFERENCE TO RELATED APPLICATIONS

The present patent application is related to our co-pending applicationentitled “A Method For Processing In Situ Inspection Reformer TubeData,” U.S. application Ser. No. 10/707,629 filed Dec. 25, 2003, whichis incorporated by reference as if fully set forth herein and “A Methodfor Reformer Tube In Situ Inspection Radius Calculation”, U.S.application Ser. No. 10/707,630 filed Dec. 25, 2003, which isincorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to inspection of materials, and moreparticularly to the inspection of the surface of materials for creep,metal dusting, irregularities, and manufacturing flaws. With stillgreater particularity the invention pertains to the inspection of theinterior of cylindrical surfaces such as reformer tubes used in chemicalprocessing.

2. Description of the Related Art

Reformer tubes are used in many chemical processes. Examples includetubes used to produce ammonia, methanol, hydrogen, nitric and sulfuricacids, and cracking of petroleum. Reformer tubes, also called catalysttubes, are one of the highest cost components of such plants both incapital and maintenance. A typical installation consists of severalhundred vertical tubes. These tubes represent a significant cost forreplacement and can be a major source of plant unavailability ifunplanned failures occur.

Such tubes are frequently subjected to pressure changes and contact withcorrosive substances. Under such situations creep, metal dusting, andsurface irregularities frequently develop. If left untreated, creep willdevelop into cracks that will propagate leading to failure of the tube.

The plant operator is faced with balancing production needs against tubelife and risk of tube failure. The Inner Diameter (ID) of these reformertubes is generally between 76 mm (3.0 inches) and 127 mm (5.0 inches).During plant operation the catalyst filled tubes are externally heatedto allow the reforming reaction to occur. One of the major concerns inplant operation is that the reformer tubes operate at an elevatedtemperature such that they are susceptible to a failure mechanismreferred to as “creep”. This condition exists due to the elevatedtemperatures and stresses imposed by internal pressure, thermalgradients, and mechanical loading cycles. Being able to identify andlocate such damage in its early stages is essential for optimizing plantoperation.

Conventional Nondestructive Examination (NDE) inspection techniquescurrently applied to reformer tubes are geared to finding creep damagein the form of internal cracking. However, with the trend towards largertube diameters and longer intervals between turnarounds, the detectionof such defects may not allow for sufficient time for forward planningof tube replacements. Also, such “end of life” techniques do not allowany differentiation between the “good” tubes. Early detection ofunderutilized tube life can prevent the lost opportunity on bothunrealized production through running them too cool and tube life“giveaway” if good tubes are discarded prematurely.

Typically, destructive testing is used on a small number of tubesremoved from the reformer to try and determine the absolute liferemaining. Whatever the method is used, the results are used on a samplesize that is not statistically valid. It is preferable that all thetubes be surveyed with a NDE technique to characterize their relativecondition in order to make sense of the absolute condition assessmentprovided by the destructive testing.

Reformer tubes undergo creep strain, in the form of diametrical growth,on the first day that they are fired. The ability to accurately measureand record this growth means that the tubes' condition can be monitoredon day one. Therefore, not only can individual tubes be retired fromservice at an appropriate time, but also the reformer as a whole can beassessed for performance.

Another problem that can occur in reformer tubes is metal dusting. Metaldusting is a condition where the process stream attacks the interior ofthe reformer tube with subsequent, significant metal loss. This can besevere enough to be the life limiting condition for the tube. Typically,the metal dusting damage is limited to a 360° circumferential bandaround the catalyst tube's interior surface where the criticaltemperature range exists.

External diameter measurements have been used but they are limited asthe automated devices only measure across one diameter and are oftenaccess-restricted by tube bowing. Manual measurements are too timeconsuming to provide more than a few readings per tube. No externalmeasurement method can provide diameter growth data at or through thereformer refractory. External measurements are inherently less preciseas they are based on a cast surface rather than the internal machinedsurface and do not take into account the effects of oxide shedding. Themost accurate growth measurements are obtained when ‘as new’ baselinedata has been taken prior to the tube being fired for the first time.However, if this is not available by using the top portion of the tubethat is operating outside the creep temperature as a reference diameter,the growth profile of the tube can be determined at any stage in itslife.

Accordingly, there is a need for an automated method and apparatuscapable of examining the internal surfaces of reformer tubes. The methodshould be nondestructive and provide both absolute and relativeinformation on tube profile.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstancesand has as an aspect a method for nondestructive automated inspection of100% of the tube length from the reformer. Included within the scope ofthe invention is a probe capable of moving through the tubes whereinspection is required. The probe includes a light source and a meansfor detecting the reflection of the light on the surface of the reformertube. The reflected light produces an electrical signal from which theprofile and reflectivity of the surface of the tube may bereconstructed. Signal processing means are provided to reconstruct thesurface from the signal.

Another aspect of the present invention includes a method for processinga signal that includes X, Y, and intensity data sets for each pixel of asensor from an image sensor receiving a substantially ring shaped image.The method includes converting a signal having an X position, a Yposition and an intensity component to a signal having an angle, aradius, and an intensity and filtering out signal sets that do not havea radius greater than a predetermined radius value.

A further aspect of the present invention includes a method forinspecting a reformer tube for chemical processing for damage such ascreep and metal dusting. The method includes the steps of focusing acoherent light beam onto an interior of a tube or piping and detectingat least a portion of a reflection of the light beam from the tubing byconverting the detected light beam into an electrical signal and theprocessing of the electrical signal to determine a radius of tubeunder-going in situ inspection.

An embodiment of the invention employs a solid-state laser diode. Afocusing lens is located in front of the diode to focus the laser at aspot on the surface of the tube sought to be inspected. The diode andfocusing lens are rotatable within the tube to allow the spot to form aring as they are rotated. As the probe moves through the tube the spotscans the entire surface. A photo detector is arranged behind an imaginglens to detect the intensity of the spot. Both the detector and theimaging lens rotate in the same fashion as the laser diode and itsfocusing lens. The optical paths are selected so that the diode, photodetector and surface of the tube form a triangle. The distance betweenthe detector and diode is fixed. This results in the reflected spotmoving on the surface of the photo detector in proportion to thedistance to the internal surface of the tube. Signal processing meanscan then use that information to reconstruct a three dimensional imageof the internal surface of the tube. The image may either be displayedon a monitor or printed for later review.

With present technology a 15-meter tube can be inspected within threeminutes. An inspection such as this will provide over 1,000,000 radiusreadings. The method provides means to compress this information toallow easy manipulation and analysis.

A further aspect of the present invention employs a laser or lightemitting diode (LED) and a cone shaped reflector to project a ring ofillumination on the interior of the tube to be inspected. Acharge-coupled device (CCD) is arrayed so as to scan the ring and reportthe reflectivity and profile. Signal processing circuitry reconstructsan image of the interior of the tube.

The use of the internal laser mapping technique is not only useful inpreventing tube failure but has huge potential in optimizing productionfrom the whole tube set without sacrificing reliability.

Additional aspects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theaspects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts (elements).

FIG. 1 is a block diagram of a first embodiment of the Invention;

FIG. 2 is diagram of the optical components of the FIG. 1 embodiment;

FIG. 3 is a perspective detail view of the probe of the invention;

FIG. 4 is a block diagram of a second embodiment of the Invention; and

FIG. 5 is diagram of the optical components of the FIG. 4 embodiment.

DETAIL DESCRIPTION

FIG. 1 is a block diagram of an embodiment of the invention. Componentsmay be either hardware components or software modules as describedbelow. The probe includes a light source 1. The purpose of the lightsource 1 is to project a spot of light on the surface (not shown) to beinspected. Light source 1 is typically a laser diode or light emittingdiode (LED). A light source controller 2 is connected to light source 1.Controller 2 sets and controls the optical power level of light source1. The power level may either be fixed or varied to produce a presetsignal level.

A position sensitive photo detector (PSD) 3 is situated so as to detectthe spot made by light source 1. Photo detector 3 may be a lateraleffect photodiode, photodiode array, or charge coupled device (CCD).This description assumes the device chosen for 3 is a lateral effectphotodiode. Detector 3 may have either one or two axes, dependant uponthe specific measurement geometry. In this description only a singleaxis detector and associated lens (not shown) is used. Similarly a 2Ddetector may be used for 3 if the light beam from light source 1 isrotated, by means of a rotating mirror, and detector 3 is fixed. Anamplifier filter 4 is connected to detector 3. Amplifier/filter 4converts the small signal currents generated by detector 3 intovoltages. A filter sets the bandwidth of the system.

The required bandwidth is determined by a combination of the speed ofprobe spin and the required sample rate. Amplifier and filter may becombined into a single unit by inserting active components into adifferential amplifier to produce an active filter. A suitable amplifiermay be an integrated circuit differential amplifier such as a AD712. Afeedback path is provided between amplifier/filter 4 and light sourcecontroller 2 to allow control of light source 1 dependant upon theintensity of signal received at detector 3. One or more gain systems 6may be connected to the output of amplifier/filter 4.

This embodiment shows 2 gain systems (5 and 6) each providing adifferent level of gain. The addition of one or more additional gainsystems increases the dynamic range of the system and allows rapidchanges of surface reflectivity to be measured. The outputs of theseveral gain stages are recorded simultaneously, and the largest valuethat is below saturation is used. Several gain systems may be connectedin parallel to provide usable signals in all situations.

A normalization and synchronization processing circuit 7 is connected tothe output of gain system 6. The first function of system 7 is to selectthe signal from multiple gain systems 6 with the maximum dynamic rangewithout saturation. The second function is to convert the individualdetector readings to a calibrated measurement of the distance betweenlight source 1 and the surface to be scanned. For a ID detector thecalibration may be found by solving equation 1 as the follows:$\begin{matrix}{{Measurement} = {g \cdot \frac{v_{1} - v_{2}}{v_{1} + v_{2}}}} & {{EQ}.\quad 1}\end{matrix}$

In the equation, ν₁ and ν₂ are the current readings from either end ofdetector 3. (g) is a calibration function used to remove non-linearityin the detector and optics. (g) may be determined empirically byscanning calibrated tube samples of various diameters and using theresultant data points to find coefficients of the function (g). As analternative to the calculation using (g) in the above equation, a lookuptable with some form of interpolation may be used. In order to eliminateelectronic drift the system periodically turns light source 1 off andmeasures electronic offset voltages. The offset voltages are thensubtracted from subsequent readings made with light source 1 on.Normalization and synchronization processing circuit 8 also measures thesurface reflectivity. The reflectivity of the surface is computed fromthe detector signal level, gain, and light source power level.Variations in surface reflectivity can provide useful information aboutthe surface. Normalization and synchronization processing circuit 7 alsocollects data from a rotational encoder in 8. The correlation of thesignals from encoder in 8 and from photo detector 3 assures equallyspaced samples around the circumference of a tube.

Two motors 11 and 12 move the probe. The first motor 11 rotates theprobe within a tube. A motor drive circuit 13 controls motor 11. Encoder8 is connected to motor 11 allowing determination of the absoluterotational position of the probe. The output of encoder 8 is connectedto normalization and synchronization processing circuit 7. A secondmotor 12 provide axial positioning of the probe. A second motor drivecircuit 14 controls motor 12. An axial incremental encoder 15 connectedto motor 12 provides information on the axial position of the probe inthe tube.

A system data storage display and control module 16 provides overallcontrol of the probe. Module 16 receives information on the distancebetween light source 1 and the surface sought to be inspected andsurface reflectivity from normalization and synchronization processingcircuit 7. Module 16 also receives information about the axial positionof the probe from encoder 15. Module 16 controls the rotational positionof the probe in the tube by sending an on and off signal to rotationalmotor drive circuit 13. Module 16 also controls the axial position bysending on/off and forward/backward signals to axial motor controlcircuit 14.

FIG. 2 is diagram of the optical components of the FIG. 1 embodiment. Alight source I produces beam of light. Light source 1 is usually a diodelaser but could be a light emitting diode in special applications. Acollimating lens 21 downstream of light source 1 converts the lightemitted by light source 1 into a collimated beam which does not spreadto any appreciable extent over the inspection range 22′-22″. The beamproduces a target spot 22 where it impacts the target surface 23. Aphoto detector 27 is mounted at an angle to the optical train ofcomponents 1, 21, and 22. The angle is detected such that the imagedspot at 26 is in focus over the measurement range 22′ to 22″. Photodetector 27 is usually a lateral effect photodiode array or chargecoupled device (CCD) photo detector. Photo detector 27 may either be aone dimensional (ID) or two dimensional (2D) device. If photo detector27 is a 2D device additional information may be generated at the expenseof greater bandwidth. An imaging lens 24 is mounted in front of photodetector 27. Imaging lens 24 projects an image of the surface of target23 onto photo detector 27. The image projected onto photo detector 27includes an image 26 of the spot 22 where the collimated beam impactsthe target. The position of imaged spot 26 varies with the distance fromlight source 1 to target 23 due to parallax. If, for example, thesurface of target 23 is at 22′ the imaged spot is at 26′. Similarly, ifthe target is at 22″the imaged spot will be at 26″. The result is thatimaged spot 26 moves back and forth across the surface of photo detector27 in an amount relative to the distance between target surface 23 andlight source 1. Photo detector 27 thus generates an electrical signalcontaining information about the distance between 1 and 23.

The complete optical system, as described, is rotated around the centralaxis of the probe in order to scan the complete circumference of thetube. Other embodiments modify the basic optical system to reduce theneed for slip rings for the electrical signals required by the laserdiode and detector. By locating the laser diode source and collimatinglens on axis with the probe longitudinal axis and using a rotating 45°mirror to deflect the light beam at a right angle to the probelongitudinal axis, the beam can be made to scan the circumference of thetube. A second mirror and imaging lenses are also rotated with the firstmirror, to form an image of the light spot onto a stationary 2D PSD.This approach has the advantage of eliminating slip rings from theprobe. The disadvantage is that the 2D PSD provides 4 outputs instead of2, and requires more processing to compute the radius data. Anotherdisadvantage of this method is that a transparent tube or windows in thehousing are required to support the laser diode and detector, whilestill allowing a light path. The window or transparent tube are subjectto scratches or dirt which provide reflection paths for light leakagebetween the laser diode source and the detector. These light leakagepaths cause errors in the radius measurement Also, the electrical wiresnecessary to connect to either the diode or detector must cross the pathof the light beam at some point in the rotation of the lens/mirrorassembly. Other variations of the optical arrangement are possible. Theembodiments described herein are not intended to limit the scope of theinvention, but rather are for illustrative purposes. [FIG. 3 shows adetailed profile view of the probe of an embodiment in this invention.The probe consists of a rotating optical head 30 mounted to a body 31.

The relative size of the reformer tubes present other challenges tolaser-optical probe design. Previous probes of this type have been forsmaller diameter tubing, up to 2-inches in diameter. For larger diametertubes, such as reformer tubes, the weight and inertia of the probe andits rotating components must be reduced to make the approach practical.In one embodiment of the system, the probe head 30 is spinning at 1800rpm. Replacing a metal spinning head with one made of Delrin™, anengineering plastic made by Dupont, provides weight and inertiareduction while maintaining structural strength, thermal stability, andimpact resistance.

The probe body 31 is made relatively small compared to the diameter ofthe reformer tube. This allows weight reduction, and has the benefit ofallowing the same probe body to be used in several different tube sizesby changing the centering spring assemblies, and the probe head. Weightreduction is important in the reformer tube application because theprobe is drawn through the tube by a motorized positioning system.Reducing the weight reduces the size and cost of the positioning system.

A tether and electrical connections are made to the probe throughconnector 32. Electrical connections between the connector and theoptical head are made through the probe body by means of an internalslip-ring. Probe rotation is by means of a motor inside probe body 31.Centering rings 35 are spring loaded arms with non-metallic wheels tohold the probe in the center of the tube, and allow for axial motionthrough the tube.

Reformer tubes are made of special alloys to withstand the temperatureand pressure regimes to which they are subjected. During normaloperation, portions of reformer tubes operate at or near the structuralstability limit of the tube metallurgy. If the probe leaves any tracesof other metals on the inner tube surfaces, such as aluminum or lead,the traces of these metals will enter the pores of the tube wall andcause rapid cracking and failure of the tube. Therefore, it is importantthat only non-metallic components be used where the probe is in contactwith the tube surface. The probe's centering spring mechanism 35contacts the sides of the tube with wheels 36 made from Delrin™, anengineering plastic with metal-like properties.

One of the problems that affects accuracy in PSD based lasertriangulation systems is when unintended reflections cause additionallight to impinge on the sensor. These reflections arise when lightreflects from the surface being measured, bounces off other surfaces andenters the detector from various angles. Because the PSD sensor measuresthe centroid of the light imaged on its surface, reflections cause askewing of the image centroid. The present invention minimizesreflections by placing the laser 37 at the front of the probe head andin front of the detector 38. In contrast to designs with the laserbehind the detector, this reduces the exposure of the detector to lightreflections off the probe head 30, body 31, and centering springassemblies 35.

FIG. 4 is a block diagram of an alternate embodiment of the invention.This embodiment projects a ring of light onto the interior surface ofthe reformer tube. The ring is then scanned with an array of lightsensors to produce and reconstruct an image of the interior of the tube.

A light source 40 is connected to a power controller to maintain a lightlevel sufficient to be sensed by an image detector. Typically lightsource 41 is a laser diode with output in the infrared or visibleportion of the spectrum. A light detector 42 is positioned in such amanner as to view an image of the ring of light. Light detector 42 is atwo dimensional array of photosensitive cells. Most commonly detector 42is a Charge Coupled Device (CCD) array of photocells. Such arrays arecommonly used in video cameras. Array 42 is divided into individualpixels each represented by an X coordinate and a Y coordinate. Thesignal from each pixel is proportional to the intensity of light fallingon that pixel. The detector is controlled by a timing and control module43. In general, module 43 scans the array in a line-by-line fashion.Each individual line is moved to an output register. The individualpixels are then shifted out in a serial operation. The CCD array is ofthe Frame Transfer type which uses two identical CCD arrays, one forscanning and one for storage. The second array is shielded from lightand acts a buffer to allow reading an image while a second image isbeing formed on the first array.

A typical sensor is a 512×512 array having 262,144 elements or pixels.Typically, there are additional light shielded pixels in the array whichprovide buffering of the active pixels. This increases the number oftotal pixels which must be read. A typical 512×512 array requires aclock speed of 80 Mhz to read out with time for the buffer pixels,transferring the frame, etc., for a 120 Hz frame rate. Some arrays havea split output structure, so that two pixels are read at a time. Thisreduces the clock rate to 40 Mhz, but requires two parallel outputprocessing channels. In tested prototypes the ring image has a thicknessof 3-5 pixels. At the maximum radius the number of pixels actually usedis provided by equation 2 as follows:2·π·r·5≢8 k pixels   EQ. 2

Where r, at the maximum radius is 256 for a 512×512 array. In otherwords each frame will hold about 8 k pixels of useful information.

During use, array 42 converts the image to an array of intensity values.The Analog to Digital Converter 44 connected to Array 42 converts thisanalog signal to a digital one. An eight-bit A to D converter has beenfound suitable for 44. The signal next goes to a Look-Up-Table (LUT) 45to convert the Cartesian X, Y coordinates received from the Timing andControl Module 45 into radial coordinates r, θ. LUT 45 may be a logicalarray or an addressable device such that when an X and Y address isinput, a value for r and θ is provided. This may be done withnon-volatile memory devices such as ROM, PROM, EPROM, EEPROM, flashmemory, or a volatile memory such as static or dynamic RAM. The speed ofoperation required for this embodiment dictates the use of volatilememory, such as synchronous RAM. The access time must be under 30nanoseconds for a 512×512 array. A 256 k×18 device provides 9 bits eachfor r and θ. For a 10-bit θ, the MSB of the Y address value can be addedto θ to form 10 bits. A 9-bit θ is used for 360 points per rotation, 10bits for 720 points per rotation, for ½°resolution.

The X and Y address of each pixel is fed to the address lines of the LUTat the same time that the value of intensity for the pixel is availablefrom the A to D converter 44. Because LUT 45 is a volatile memorydevice, it must be loaded with the lookup values before use. This may bedone on power up of DSP 50 or host PC 51. LUT 45 is programmed with thecorresponding r and θ for each X and Y address of sensor 42 according toequation 3 as follows: $\begin{matrix}{{r = \sqrt{X^{2} + Y^{2}}},{\theta = {\tan^{- 1}\left( \frac{Y}{X} \right)}}} & {{EQ}.\quad 3}\end{matrix}$

The intensity value from array 42 and the r,θ values from LUT 45 aresent to a Data Range Control module (DRC) 46. DRC 46 reduces the amountof data used in further processing steps. The actual image from array 42includes only about 8 k of pixels out of a typical 256 k pixels in a512×512 array. The pixels of interest are in a circular area in theouter third of the array. The definition of the pixels of interest t isr>r_(t) where r_(t) is the radius threshold value and is the minimum rvalue of interest. No image data ever occurs at r-values less thanr_(t). DRC 46 includes logic circuitry which only passes to FIFO 47 theinformation of interest i.e. r>r_(t).

Even with the use of DAC 47 there are still too many pixels withoutuseful information for easy processing. For example in a 3-in ID pipewith a probe measuring range from 2.25 in to 2.75 in. radius and a512×512 array the measuring range will cover 85 pixels with r having arange of from 171 to 256. If r_(t) is set to 170 there are still over170,000 pixels per frame to be processed. Only the pixels that areilluminated by the light source 40 provide useful information. Sinceonly pixels with intensity over a certain threshold are of interest thatfact may be used to eliminate surplus pixels. A high-speed comparator 48is used to compare the intensity value of each pixel with a thresholdvalue I_(t). The output of comparator 48 triggers the data selection topass only the data including r, θ, and I, where I is greater than thethreshold I_(t). This reduces the data sent to FIFO to about 8 k pixels.The threshold value I_(t) is set with a DAC device 49. DAC 49 is setfrom the host system via the DSP controller 50 during calibration.

Since the actual data rate is greater than 40 MHz accordingly; a FIFO 47is used to buffer the data at that rate. Data entering FIFO 47 clocks atthe scan rate of the array 42 but is sporadic and has many gaps due tothe action of the data selection effect of DRC 46 and comparator 48.FIFO 47 buffers the data for DSP 50, which is thus able to read the dataat a slower rate. DSP 50 must still process all 8 k of data in under 8.3milliseconds in order to process 120 frames/sec. FIFO 47 will buffer oneframe of data for an 8 k FIFO or two frames for a 16 k FIFO.

The Digital Signal Processor (DSP) 50 performs the actual computation ofthe radius of the tube by finding the centroid of the imaged light oneach radial spoke θ_(k) where k indexes the angle through 360 or 720increments depending on the resolution. The centroid for each radialspoke θ_(k) is computed according to equation 4 as follows:$\begin{matrix}\frac{\sum\limits_{i}{r_{i} \cdot I_{i}}}{\sum\limits_{i}I_{i}} & {{EQ}.\quad 4}\end{matrix}$

Where r is the radius value from 0 to 255 for a 512×512 array, and I isthe corresponding intensity value for that pixel, i is the index valuefor the array of points comprising the radial spoke. In practice, istarts at a radius much larger than 0 since the image is set in theouter third of array 42. A DSP 50 of sufficient speed can perform thedivision and provide the radius value directly. If a lower speed DSP 50is used it can compute the numerator and denominator of the aboveequation and provide the values as separate outputs. A post processingoperation in host PC 51 computes the actual radius value and convertsthe output to engineering units such as inches or millimeters. Theprocessed data is sent to host PC 51 via a high-speed interface;suitable methods include serial interfaces such as RS232, RS485, USB, orIEEE-1394 (Firewire) or parallel interfaces such as a PC parallel portor EPP.

Host PC 51 receives the data from the probe processing system, and doesany post processing of the data and formats it for storage on hard diskor removable media storage and displays the data on a graphics screen.

FIG. 4 illustrates an implementation having a single processing channel.For an image sensor with a dual output structure, another channel ofprocessing is added with another A/D converter, LUT, Data RangeController, comparator, and FIFO.

FIG. 5 is a front elevation view of the optical system of the FIG. 4embodiment. The components are located in a tube 64 to be inspected. Alaser diode 61 is located at the center of tube 64 in such a manner thatthe light emitted by diode 61 is parallel to the axis of tube 64. Acollimation lens 62 is located on said axes to focus the light on theinterior surface of tube 64. A cone mirror 63 is located coaxial todiode 61 and lens 62 to form the light emitted from diode 61 andcollimated by lens 62 into a ring 65 on the surface of tube 64. Mirror63 is preferably a parabolic conical mirror to aid in focusing the beamon the interior surface of the tube. An imaging lens 66 coaxial withdiode 61 lens 63 and mirror 63 is situated in such a manner as toproject an image of ring 65 onto the surface of an imagining array 67.Imaging array 67 senses the image projected onto its surface andconverts the image into electrical signals.

The above examples and embodiments are exemplary only the inventionbeing defined solely by the attached claims.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the “Method And ApparatusFor In Situ Inspection Of Reformer Tubes” of the present invention andin construction of this invention without departing from the scope orintent of the invention. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A device for inspecting the interior of metal tubes used in chemicalprocessing for the presence of metal dusting and creep comprising asource of light adapted for focusing a spot of light on the interiorsurface of said tubes; means for focusing said light source on theinterior surface of said reformer tube, and a detector for detectingsaid spot of light focused on the interior of said reformer tube, andmeans for centering said source and said detector in the center of saidtube; and means for moving said detector, source, and centering meansthrough said detector tube.
 2. A device for inspecting the interior ofmetal tubes used in chemical processing for the presence of metaldusting and creep as in claim 1, wherein said means for focusing saidspot on the surface of said reformer tube includes a laser source andoptical detector in a rotating head for rotating said spot around theinner circumference of said reformer tube.
 3. A device for inspectingthe interior of metal tubes used in chemical processing for the presenceof metal dusting and creep as in claim 2 wherein said source ispositioned forward of said detector in a direction away from the probebody and centering device.
 4. A device for inspecting the interior ofmetal tubes used in chemical processing for the presence of metaldusting and creep as in claim 1, wherein said centering device isadapted for use in reformer tubes by preventing chemical interactionwith the inside surface of said reformer tube.
 5. A device forinspecting the interior of metal tubes used in chemical processing forthe presence of metal dusting and creep as in claim 4, wherein saidcentering device is constructed so that all surfaces which maypotentially contact the interior of said tube are constructed out ofnonmetallic materials.
 6. A device for inspecting the interior of metaltubes used in chemical processing for the presence of metal dusting andcreep as in claim 1, wherein said focusing means includes a conicalmirror for projecting a focused ring of light on the interior surface ofsaid reformer tube.
 7. A device for inspecting the interior of metaltubes used in chemical processing for the presence of metal dusting andcreep as in claim 6, wherein said conical mirror is parabolic to focussaid ring to a small circumferential line.
 8. A device for inspectingthe interior of metal tubes used in chemical processing for the presenceof metal dusting and creep as in claim 6, further comprising signalprocessing means to reduce the bandwidth of information transported outof said reformer tube.
 9. A method for forming a profile of the radiusof the interior of a tubular structure comprising the steps of;producing a light beam on the axis of said tube, collimating said beamto focus on the surface of said tube, forming said collimated beam intoa ring on the surface of said tube, projecting an image of said ringonto the surface of a sensor and moving said ring down the axis of saidtube.
 10. A method for forming a profile of the radius of the interiorof a tubular structure as in claim 9, further comprising the step ofreflecting said beam off the surface of a conical mirror.
 11. A methodfor forming a profile of the radius the interior of a tubular structureas in claim 9, further comprising the step of reflecting said beam offthe surface of a conical mirror with a parabolic surface for maintainingfocus of said beam on the expected tube diameter.
 12. A method forforming a profile of the radius of the interior of a tubular structureas in claim 9, further comprising the steps of, reflecting said beam offa mirror at the axis of said tube, and rotating said mirror to produce aring of light on the surface of said tube.
 13. A method for inspecting areformer tube for chemical processing for damage including creep andmetal dusting, comprising the steps of: focusing a coherent light beamonto an interior of said tube and detecting at least a portion of areflection of said light beam by converting the detected light beam intoan electrical signal and processing said electrical signal to determinea radius of said tube.
 14. A method for inspecting a reformer tube forchemical processing for damage including creep and metal dustingaccording to claim 13, comprising the further step of rotating saidlight beam by reflecting at least a portion of said light beam it off asurface of a rotating mirror.
 15. A method for inspecting a reformertube for chemical processing for damage including creep and metaldusting according to claim 14, wherein said detecting step is preformedby a charge coupled detector array.
 16. A method for inspecting areformer tube for chemical processing for damage including creep andmetal dusting according to claim 14, wherein a detector array ispositioned aft of said light beam.
 17. A method for inspecting areformer tube for chemical processing for damage including creep andmetal dusting according to claim 13, comprising the step of reflectingsaid light beam off a conical mirror to focus said light beam into aring on the interior surface of said tube.
 18. A method for inspecting areformer tube for chemical processing for damage including creep andmetal dusting according to claim 17, further comprising the step ofprocessing said signal in said tube to at least one of filtering andenhancing collected data.
 19. A method for inspecting a reformer tubefor chemical processing for damage including creep and metal dustingaccording to claim 17, wherein dynamic range is increased by the use ofone or more parallel gain stages.
 20. A device for inspecting theinterior of metal tubes used in chemical processing for the presence ofmetal dusting and creep according to claim 1, wherein the rotatingportions of said device are adapted for high speed operation above 1500revolutions per minute.
 21. A device for inspecting the interior ofmetal tubes used in chemical processing for the presence of metaldusting and creep according to claim 20, wherein said high speedoperation is achieved by using a material that is substantially lighterthan metal for the body of said device.
 22. A device for inspecting theinterior of metal tubes used in chemical processing for the presence ofmetal dusting and creep according to claim 21, wherein said body issubstantially smaller than the inside diameter of the tube sought to beinspected allowing inspection of several tube diameters.